Many applications in the field of chemical and biological requires separation of chemical components prior to or after reacting the chemicals. Examples of reactions requiring separation of components include organic, inorganic, biochemical, and molecular reactions. Examples of chemical reactions include thermal cycling amplification, such as polymerase chain reaction (PCR), ligase chain reaction (LCR), isothermal nucleic acid amplification, self-sustained sequence replication, enzyme kinetic studies, homogeneous ligand binding assays, affinity binding assays, and more complex biochemical mechanistic studies. Conventional separation techniques include electrophoresis, such as capillary electrophoresis, synchronized cyclic electrophoresis, and free flow electrophoresis. Conventional separation techniques also include isoelectric focusing (IEF), hybridization, liquid and gas chromatography, molecular sieving and filtering.
Of increasing interest in the field of chemical separation is the use of devices that include an integrated reaction chamber and separation regions. Such integrated devices provide a number of advantages over conventional devices in which one transfers a fluid sample between a reaction apparatus and a separation device and/or vice versa. For example, where the chemical reaction and separation steps are performed in a single integrated device, one may avoid contamination and crossover of sample or reaction products. In addition, an integrated device may allow for substantially faster sample processing and analysis.
Recent efforts to integrate processing and analytical functionalities in a single device, especially in the field of MEMS, microfabrication, and microfluidics, have resulted in the development of devices that include multiple substrates bonded together. The substrates are usually bonded with adhesives, or by heat sealing, fusion bonding, or anodic bonding. These multi-substrate devices typically include a reaction chamber that is connected to a separate separation component, such as a capillary tube containing a suitable electrophoresis gel, by an adhesive such as epoxy. Alternatively, these multi-substrate devices have reaction chambers and separation channels etched into a plate and a cover bonded over the top of the plate. For example, U.S. Pat. No. 5,849,208 to Hayes et al. and U.S. Pat. No. 6,979,424 to Northrup et al. disclose such devices. However, these prior art devices do not address sample preparation prior to reacting the chemicals. This is a particular difficult problem because certain chemicals used in pre-reaction sample preparation may detrimentally affect the reaction itself.
One application of particular interest is the polymerase chain reaction (PCR). Since the technique was first described two decades ago, PCR has become an essential tool in the field of genetic analysis, providing an in vitro method to amplify DNA sequences of interest. However, while conventional techniques are improving in speed, they are still time consuming (1-3 h per amplification), and the reagents are expensive at the volumes needed for manual transfer of samples between pre-treatment, amplification, and analysis steps. Furthermore, the conventional method of PCR product analysis, gel electrophoresis, has similar limitations in time and reagent volumes.
An solution to these problems was proposed by Manz et al. (Sens. Actuators B, 1990, 1:244-248) in the form of miniaturized total chemical analysis systems (R-TAS), where microfabricated fluidic networks could be utilized for sampling, pre-treatment, and analysis/detection of samples as well as the transport between the different domains. The development of these integrated microfluidic systems for genetic analysis has been a major research focus since the systems were proposed, with particular motivation from the clinical and forensic sciences. However, after more than a decade and a half after Manz et al.'s proposal, no bona fide microfluidic device has been demonstrated that is capable of nanoliter flow control with comprehensive sample pretreatment integrated with an analytical step for genomic analysis of whole blood.
Therefore, there remains a need for a μ-TAS capable of pre-reaction sample treatment, reaction, and post-reaction chemical separation all on one chip; and methods of efficiently operating such μ-TAS to eliminate poisoning of the reaction by reactants used in the sample treatment.